64 MEASUREMENT OF HIGH TEMPERATURES. 
The cylindrical reservoir, or retort proper, shown at A, Fig. 4, was 
made by screwing cast iron caps N JV, (7 0, upon the ends of a piece 
of iron pipe 6 inches long and 6 inches in diameter. A piece of 1-inch 
iron pipe, 2), fitted in the upper cap 0, and extended upward to an 
elbow, F, and similar pipe, B, which latter passed out through the side 
wall of the anthracite furnace at 0. Thence the pipe B extends 
through the J at J J, 18 inches, into the iron pipe H 27, which is 
screwed into the other end of the T. The third opening of the T is 
fitted with the short outlet pipe 2l, 1 inch in diameter. A cap, G, 
closes the whole apparatus except the outlet at K. A small iron pipe, 
F F, passing through the cap G, and extending 15 inches into the 
interior tube B 2>, and closed at its inner end was intended to receive 
the thermo-element. A perforated tube burner, L LL, Fletcher system, 
placed beneath the pipe R 27, was intended to prevent the solidification 
of the metal therein and consequent stoppage of the circulation of vapor. 
We hoped to be able with this apparatus to obtain a region of constant 
temperature in the inner end of the tube F, which would be surrounded 
by two distinct jackets of the vapor of zinc. We expected the action 
to be as follows : 
The vapor rising from the boiling zinc in the retorts, to pass through 
2) and B B, out past the end of F, out of the end of B into H 27, 
thence backward through 27, and out at 2T, either still in the state of 
a vapor or condensed to a liquid in 27. 
Two difficulties made the apparatus impracticable. Whereas melted 
zinc or zinc vapor has little or no solvent effect upon iron, still zinc just 
at the boiling surface or at the point of condensation of the vapor does 
dissolve iron in considerable quantities. This action of the boiling zinc 
soon eats through the iron walls of the retort and makes the whole ap- 
paratus very short lived. Moreover, the spontaneous combustion of 
zinc vapor on coming to the air inevitably results in stopping up the 
outlet, causing the destruction of the apparatus. These objections, to- 
gether with other minor ones, led to the abandoning of this form and 
ultimately of all forms constructed on a similar principle. 
The principle next applied was that of downward distillation through 
the bottom of the crucible, a system that had already proved very good 
for mercury and some other substances, and which has been touched 
upon in an earlier part of this chapter. 
The particular form ultimately constructed is shown in vertical cross- 
section in Fig. 6 and in vertical longitudinal section in Fig. 5. In this 
case the furnace formed an essential part, and was constructed simulta- 
neously and as part of the whole. It covered 5 x 3 J feet on the floor and 
stood 5 feet high. It was built of brick, lined with fire-brick, on the 
double-reverberatory principle, entirely symmetrical. Each side was 
provided with a fire-box, A (Fig. 5), a grate, 0, ash-box, B, ash-door, O, 
blast inlet, Q, and fire-box door at 2>. The zinc was contained in the 
(718) 
